Reading data from a process environment, such as, for example, from a field, via input signals that are provided by appropriately arranged signal generators, that is particularly by switches [and] sensors, puts demands on the requirements for error recognition and the failure behavior of a circuit constructed for this purpose as well as of the periphery.
Particularly in the case of safety-relevant data in the field of safety technology, these requirements must meet, for example, the standards according to DIN EN 954-1 or according to IEC 61508. To satisfy such requirements, complex, conventionally two-channel, structures of the input circuit are required, which entails high cost for producing the circuit and for providing the circuits for the periphery, that is, particularly with respect to the wiring to the signal generator, for example, to a safety switch. Such circuits consequently have a very complex structure and as a result are also cost intensive. Due to the increased need for component elements, these circuits are additionally also disadvantageous with regard to their availability.